(1) Field of the Invention:
This invention relates to a process for quickly and continuously producing cheese curds useful in the production of varieties of cheese and also to a process for producing cheese from the cheese curds.
(2) Description of the Related Art:
Cheese curds have heretofore been produced by ingeniously using the actions of both a lactic acid bacterium starter and a milk-coagulating enzyme, more specifically, by adding both the lactic acid bacterium starter and the milk-coagulating enzyme to milk and conducting for a prescribed time both formation of the acid by the starter and a reaction by the enzyme. The acid is required for the formation of curds, while the reaction plays a role in the coagulation. This reaction is a primary enzymatic reaction and converts kappa casein to para-kappa casein. This conventional process however requires a long time from the addition of the lactice acid bacterium starter and milk-coagulating enzyme to the coagulation and molding, namely, for curd making. Moreover, it also requires strict control of curd-making conditions and skill, which are inherent to each variety of cheese. The conventional process is accompanied by another problem, that is, a production-related limitation is imposed on the conventional process so that for mass production, large facilities such as vats are needed and the production has to be conducted batchwise. With a view toward solving such problems, it has been attempted to continuously produce cheese curds, for example, by using concentrated milk or ultrafiltered milk or inducing low-temperature rennet action (the primary enzymatic reaction referred to above) as will be discussed below. Some of such attempts have been practiced on a production scale. Under the circumstances, none of these attempts have however successfully solved the aforementioned problems.
Namely, the production of cheese curds from UF (UF means ultrafiltration, which will be called "UF" hereinafter) concentrated milk goes back to the MMV process described in French Patent 2052121 published in 1971. It is reported in Japanese Language Laid-Open Publication (PCT) No. 501932/1984 that for the production of cheese curds from UF-concentrated milk, a continuous process has been developed by adding a lactic acid bacterium starter and a milk-coagulating enzyme to UF-concentrated milk, allowing it to coagulate successively in a certain number of vessels and then taking it out of the vessels, in other words, continuously conducting its coagulation in small batches, or conducting the coagulation on a belt conveyor or the like for a period substantially equal to the period required for the coagulation by the milk-coagulating enzyme.
Another approach is described, for example, in U.S. Pat. No. 4,689,234 issued Aug. 25, 1987, in which starting milk is partially acidified and then concentrated by UF or DF (DF means diafiltration, which will be called "DF" hereinafter), the pH of the thus-concentrated milk is lowered by a lactic acid bacterium starter, rennet is added to the concentrated milk, and the resultant mixture is charged in a continuous curds former to continuously form curds without heating.
These processes require coagulation time by a milk-coagulating enzyme. Since concentrated milk is caused to coagulate as is, they also require processing such as cutting and cooking to separate out trapped whey.
To cope with this problem, it has also been proposed to conduct the coagulation after lowering the water content of concentrated milk to a prescribed level by evaporation as disclosed in U.S. Pat. No. 4,401,679 issued Aug. 30, 1983 and Japanese Patent Publication No. 88839/1986.
In addition, Japanese Patent Publication No. 41346/1977 and U.S. Pat. No. 3,653,919 propose the formation of curds by causing rennet to act on evaporation-concentrated milk, which is not UF-concentrated milk, at 25.degree. C. for about 12 minutes to conduct the primary enzymatic reaction sufficiently, lowering its temperature to 7.degree. C. and then causing it to coagulate in a calcium chloride solution of 25.degree.-45.degree. C.
On the other hand, as processes for continuously producing curds, there are those using the action of rennet at low temperature such as the Dutch Ede process [J. Ubbels, J. T. van Linde: XVI Int. Dairy Congr. C, 185 (1962)], the U.S. Montoure process [J. E. Montoure: Proc. 31st. Ann. Mtg. Wash. State Univ. Inst. Dairy, 56-60 (1962)] and the process proposed by Berridge [N. J. Berridge: Dairy Engng., 80(3) 75, (4)130, (5)161, (6)207,(1963)]; those causing rennet at low temperature to act on concentrated milk such as the French Huntin-Stenne process [Dairy Ind., 30(9), 709 1965)]; and the "Paracurd" process disclosed in 1946 (see U.S. Pat. No. 3,899,596 and U.S. Pat. No. 3,616,536). In each of these processes, rennet is caused to act at low temperature on concentrated milk whose pH has been lowered to a prescribed level by a lactic acid bacterium starter, and the resultant mixture is mixed with a predetermined amount of hot water to heat the former.
These processes are also accompanied by problems such that a culture time is needed for the lactic acid bacterium starter, cooling is indispensable for the treatment with rennet and a time is required until the primary enzymatic reaction is completed.
The above-described processes for the continuous production of cheese curds all require a time sufficient to allow the primary enzymatic reaction by the lactic acid bacterium starter and milk-coagulating enzyme, said reaction playing a role in the coagulation, to proceed to a substantial extent. They also require a rather complex operation.
With a view toward reducing the time required for the culture of a lactic acid bacterium, it has also been proposed to conduct direct acidification by the addition of an acid in Japanese Patent Publication No. 37829/1973 and U.S. Patent Application Ser. No. 202,684. Although the acid is added at low temperature, they are accompanied by a problem which makes them improper for continuous operation, namely, they require heating in a stationary state.